Vascular catheters form very important components in modern medical treatment systems within, for example, blood dialysis treatment and intensive care. Vascular catheters of a so called multilumen type having two or more parallelly extending, mutually separated lumina, are well-known in the art. In, for example, blood dialysis, a first lumen is used as a conduit for blood flowing out of a dialysis patient to an external dialysis device, whilst a second lumen is used as a conduit for treated blood flowing from the dialysis device and back into the dialysis patient. Multilumen catheters are preferable over single lumen catheters, since they eliminate the need for several separate catheters, whereby the discomfort of the patient and the risk of infection upon insertion of the catheter are both reduced.
Vascular catheters of the above-described type, are normally inserted by means of the so called Seldinger method, named after the inventor Seldinger, who in the 1950's introduced an insertion method for vascular catheters in which a hollow syringe is first used to puncture a blood vessel, whereafter a flexible guide-wire is inserted through the syringe and further into the blood vessel to a desired position in the blood vessel of the patient, whereafter the guide-wire is retracted. The positioning in the blood vessel is normally supervised by means of ultrasound technology or other tissue scanning technology. In English-language literature, the guide-wire is sometimes named after the inventor as a “Seldinger guide-wire,” or a “Seldinger-wire.”
Vascular catheters are further provided, at a distal end-portion or “tip,” with one or more suction openings communicating with the first lumen as initially mentioned under the title FIELD OF THE INVENTION. The suction openings are located upstream—with reference to the flow direction of the blood vessel—of one or more outlet openings, that in turn communicate with second lumen. Normally, the suction openings and the outlets openings are located relatively close to each other and are thereby normally both located at or in close proximity to the distal end-portion of the vascular catheter.
One example of a known multilumen vascular catheter is described in U.S. Pat. No. 6,206,849 B1 (Martin et al). This vascular catheter comprises, except for a first outlet lumen and a second inlet lumen, also a central, separately formed third lumen designated for the guide-wire and eventual subsequent intravenous supply of medical substances. The distal end-portion is formed as a first, upstream, circular-cylindrical section in which the suction openings and outlet openings are located, and following thereafter, a downstream conical terminal section. This general outer design of the distal end-portion of the vascular catheter can be found on several of the vascular catheters that are now available on the market.
A potential problem with the common design of the distal end-portion described above, is, however, that a certain undesired recirculation may occur between the downstream outlet openings and the upstream suction openings. Part of the treated blood meant to be brought back to the blood vessel is then sucked back into the suction openings for untreated blood, resulting in a reduced treatment effect. The risk for such a recirculation is particularly increased at high flow speeds through the vascular catheters, since the suction effect from the suction openings is stronger than in cases with lower exchange flows. High flow in vascular catheters is, however, getting increasingly common within modern healthcare, due to demands for quicker treatment cycles in order to achieve a more effective patient treatment and a reduction of the patient's discomfort.
Another problem with many known vascular catheters is that they sometimes tend to adhere to the vascular wall by suction, whereby the suction openings—and sometimes also the outlet openings—are fully or partially blocked, resulting in a reduced flow through the vascular catheters. At high flows, this situation may give rise to injuries or irritations on the vascular wall, particularly when the catheter is in use for a longer period. Depending on the curvature of the blood vessel, local asymmetric restrictions, etc., the vascular catheter is normally not centered in the blood vessel during use and its distal end-portion may therefore already in an initial stage be pressed against the vascular wall in such a way that the suction openings and/or the outlet openings are blocked. In the above described known vascular catheter according to U.S. Pat. No. 6,206,849 B1 (Martin et al), both the suction openings and the outlet openings are formed in the circular-cylindrical, “straight” section of the distal end-portion, which should further increase the tendency of the vascular catheter to adhere by suction to the vascular wall. In U.S. Pat. No. 6,280,423 B1 (Davey et al), a way to design the distal end-portion of the vascular catheter so as to minimize the tendency to adhere by suction to the vascular wall during use, is described. According to this document, the problem is solved by orientating a suction opening (reference 35 in FIGS. 3a and 3b of the document) perpendicularly to the direction of flow in the blood vessel, a distance upstream of a terminal outlet opening (37). A guide-body (202) is placed downstream of the suction opening and at a certain distance from it, whereby a recess (202) for the suction opening is formed. By recessing the suction opening in this way, it cannot be blocked by direct abutment to the vascular wall. Even if this design of the distal end-portion minimizes the tendency of the vascular catheter to adhere by suction to the vascular wall, the deep recess (202) and the abrupt dimensional changes result in an undesired flow situation around the distal end-portion, which may, for example, give rise to undesired build-up of trailing formations of coagulated blood.